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A real head-scratcher: 'As-Cast' and 'As-Machined' drawings and TP with a datum feature of size

A real head-scratcher: 'As-Cast' and 'As-Machined' drawings and TP with a datum feature of size

A real head-scratcher: 'As-Cast' and 'As-Machined' drawings and TP with a datum feature of size

Note — some dimensions and GD&T callouts that are likely irrelevant to discussion aren't depicted in my mocked-up illustration. I'm fairly new to GD&T— I've learned what I know online (often trolling here — thanks for all the help!) and from our senior engineers when they have a spare minute. On to my quandry (please refer to attached mockup illustration):
  • 'A' is a datum feature of size — for better & for worse, this is a hard constraint. I promise that we had reasons for this morning.
  • The 2x through holes have to be machined in a downstream operation controlled with its own dedicated machining drawing.
  • I only care about controlling the true position of the holes with respect to the square bosses' boundaries (please refer to image),
    i.e., holes can't encroach too close to either 'left/right' boundaries of the boss through which they're drilled.
  • <I think> I can rule out using one of the 'flange' faces as a primary datum feature in the machining drawing, as our casting datum feature 'A' is a feature of size – controlling left and right holes' positions via TP to a flange face
    would not satisfy the previous requirement, as the holes have the original feature of size between them.
Bottom line: how could I control location of the 2 through-holes in the downstream machining op drawing so they're identically controlled with
respect to the material boundaries of the bosses through which they're respectively drilled?

This one has been a real head-scratcher for me. I'd appreciate any feedback you folks can give me.

RE: A real head-scratcher: 'As-Cast' and 'As-Machined' drawings and TP with a datum feature of size

Could you machine the faces of the large bosses (that you have the 1.750) dim coming from wrt to A to tighten up the 'tolerance', then make one of them the primary datum in the machined drawing for subsequent features such as the holes?

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RE: A real head-scratcher: 'As-Cast' and 'As-Machined' drawings and TP with a datum feature of size

Does the right flange get removed? The drawing is quite indistinct and I am guessing it was a JPEG rather than PNG.

Just make each face vertical (in this particular image) a FOS datum with an RFS reference to it; this will allow each hole to be nominally centered vertically; Might as well use each initial penetrating face as the primary for each hole.

I can't say about side-to-side control as the goal in that direction is unclear.

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